Method for determining the thermal expansion coefficient of ceramic bodies and glazes

Abstract

A method of measuring the coefficient of thermal expansion of a ceramic material, including the steps of applying a glaze to a substantially densified refractory body, wherein the coefficient of thermal expansion of either the glaze or the body is known, bonding the glaze to the body, putting the glaze insufficient tension to induce crazing, measuring the average distance between cracks in the crazed glaze; and determining the unknown coefficient of thermal expansion of the glaze or body.

1. A method of determining the coefficient of thermal expansion of a glaze or a refractory body, comprising:
 a) applying a glaze to the refractory body, wherein the refractory body is a substantially densified refractory body, wherein the glaze is characterized by a known elastic modulus, wherein the glaze is characterized by a known failure stress, wherein the glaze is characterized by a known glass transition temperature, and wherein the coefficient of thermal expansion of one of the glaze or the refractory body is known and the coefficient of the other of the glaze or the refractory body is unknown; 
 b) bonding the glaze to the refractory body; 
 c) putting the glaze into sufficient tension to induce crazing and to create cracks; 
 d) measuring the average distance between cracks in the crazed glaze; and 
 e) determining the unknown coefficient of thermal expansion of the glaze or refractory body according to the relationship wherein the difference between the known and unknown coefficients of thermal expansion is proportional to the failure stress of the glaze divided by the product of the elastic modulus of the glaze, the distance between the cracks in the crazed glaze, and the difference between the glass transition temperature of the glaze and the ambient temperature. 
 
     
     
       2. The method of  claim 1  wherein step e) further includes the substeps of:
 e1) determining the thermal expansion differential between the glaze and the refractory body; and 
 e2) arithmetically determining unknown coefficient of thermal expansion from the thermal expansion differential and the known coefficient of thermal expansion; 
 wherein the thermal expansion differential and the coefficient of thermal expansion of the body sum to yield the coefficient of thermal expansion of the glaze. 
 
     
     
       3. The method of  claim 1  wherein step e) includes calculating the unknown coefficient of thermal expansion from the known coefficient of thermal expansion, the firing temperature, and the average crack-to-crack distance. 
     
     
       4. The method of  claim 1  wherein the glaze has a known coefficient of thermal expansion and the refractory body has an unknown coefficient of thermal expansion; and wherein step c) includes firing the glazed body to a first predetermined temperature. 
     
     
       5. The method of  claim 4  wherein step e) further includes the substeps of:
 e1) determining the thermal expansion differential between the glaze and the refractory body; and 
 e2) subtracting the thermal expansion differential from the coefficient of thermal expansion of the glaze to yield the coefficient of thermal expansion of the refractory body. 
 
     
     
       6. The method of  claim 4  wherein step a) further comprises applying a series of glazes, each characterized by a unique coefficient of thermal expansion, to the refractory body. 
     
     
       7. The method of  claim 4  wherein step e) further includes comparing the average crack-to-crack distance in the crazed glaze to tabulated values of average crack-to-crack distance versus refractory body thermal expansion coefficients to differentials for glazes of known values at known firing temperatures to extrapolate the coefficient of thermal expansion of the refractory body. 
     
     
       8. The method of  claim 4  wherein step e) includes calculating the coefficient of thermal expansion of the refractory body from the coefficient of thermal expansion of the glaze, the firing temperature, and the average crack-to-crack distance. 
     
     
       9. The method of  claim 4  wherein step c) includes cooling the glazed body substantially from the firing temperature to a predetermined crazing temperature at a predetermined cooling rate. 
     
     
       10. The method of  claim 1 , wherein the glaze has an unknown coefficient of thermal expansion and the refractory body has a known refractory body coefficient of thermal expansion; and wherein step c) includes firing the glazed body to as first predetermined temperature. 
     
     
       11. The method of  claim 10  wherein step e) further includes the substeps of:
 e1) determining the thermal expansion differential between the glaze and the refractory body; and 
 e2) adding the thermal expansion differential to the coefficient of thermal expansion of the refractory body to yield the coefficient of thermal expansion of the glaze. 
 
     
     
       12. The method of  claim 10  wherein step a) further comprises applying the glaze to a series of refractory bodies, each respectively characterized by a unique coefficient of thermal expansion. 
     
     
       13. The method of  claim 10  wherein step e) further includes comparing the average crack-to-crack distance in the crazed glaze to tabulated values of average crack-to-crack distance versus glaze thermal expansion coefficients to differentials for refractory bodies of known values at known firing temperatures to extrapolate the coefficient of thermal expansion of the glaze. 
     
     
       14. The method of  claim 10  wherein step e) includes calculating the coefficient of thermal expansion of the glaze from the coefficient of thermal expansion of the refractory body, the firing temperature, and the average crack-to-crack distance. 
     
     
       15. A method of determining the coefficient of thermal expansion of a glaze or refractory body, comprising:
 a) applying a glaze to a refractory body to yield a glazed body, wherein the glaze and the refractory body are each characterized by a respective coefficient of thermal expansion, wherein the glaze is characterized by a known elastic modulus, wherein the glaze is characterized by a known failure stress, wherein the glaze is characterized by a known glass transition temperature, wherein one of the respective coefficients of thermal expansion is known and the other respective coefficient of thermal expansion is unknown; 
 b) firing the glazed body to as first predetermined temperature; 
 c) crazing the glaze on the glazed body to create cracks; 
 d) measuring the average distance between cracks in the crazed glaze; and 
 e) determining the unknown coefficient of thermal expansion by using the relation between the coefficient of thermal expansion of the glaze, the coefficient of thermal expansion of the refractory body, the failure stress of the glaze, the elastic modulus of the glaze, the glass transition temperature of the glaze, ambient temperature after cooling and the average distance between of the cracks in the crazed glaze. 
 
     
     
       16. The method of  claim 15  wherein step c) includes cooling the glazed body substantially from the firing temperature to a predetermined crazing temperature at a predetermined cooling rate. 
     
     
       17. The method of  claim 15  wherein step e) includes calculating the coefficient of thermal expansion of the refractory body from the coefficient of thermal expansion of the glaze, the firing temperature, and the average crack-to-crack distance. 
     
     
       18. The method of  claim 15  wherein step e) includes calculating the coefficient of thermal expansion of the glaze from the coefficient of thermal expansion of the refractory body, the firing temperature, and the average crack-to-crack distance. 
     
     
       19. A method of determining the coefficient of thermal expansion of a glaze or a refractory body, comprising:
 a) applying a glaze to a refractory body to yield a glazed body, wherein the glaze and the refractory body are each characterized by a respective coefficient of thermal expansion, wherein one of the respective coefficients of thermal expansion is known and the other respective coefficient of thermal expansion is unknown; 
 b) firing the glazed body to as first predetermined temperature; 
 c) crazing the glaze on the glazed body and creating cracks; 
 d) recording the average distance between cracks in the crazed glaze; and 
 e) determining the unknown coefficient of thermal expansion from the average distance between cracks in the crazed glaze, the firing temperature, and the known coefficient of thermal expansion. 
 
     
     
       20. The method of  claim 19  wherein step e) includes a calculation. 
     
     
       21. The method of  claim 19  wherein step e) includes reference to tabulated data.